New member, have some specific set up questions

--- Please let me know if this post should be posted in beginners forum rather than advanced ---

Hello all,

This is my first post on this form, and I wanted to just introduce myself as well as ask a couple of specific set up questions.

My name is Spencer, and live in the Phoenix Arizona metro area.

I have not set up my system yet, plan to do so as soon as its cool enough to access my attic.

So far I have 6 24 volt 180 watt panels = 1080 watts of panels, a outback m60, and a aims pure sine 1500 watt inverter. Have not purchased batteries yet. Plan to use this setup to offset my energy usage, will only use this system to power two rooms of the house (entertainment system, lights, maybe small fridge, or maybe hopefully a very small window air conditioner).


So now on to my specific questions - I am sure I will have more, I do understand the working of electricity and installing these systems but am not an expert. My questions are:

1. The panels are 24 volts, and I have 6 of them. To reduce wire size, I would like to have 3 each in series, so have 2 72 volt panel "banks".

My question is, say there are 3 panels in series on a sunny day. If one of the panels is shaded, will that cause the other 3 to change voltage to say 48 volts, or would it cause the other panels to be "worthless"? Or.... would it still put out 72 volts and just have the power output for the other 2 non shaded panel?

Not sure if I am explaining my concern correctly, please let me know if there are any questions about my write up.

2. I will be doing the panels flat (well about 3 inches high to allow heat to escape) on the roof, and my roof is slightly slanted down. The mounting equipment sold online seems to be way over priced, and the lower priced stuff looks cheap. I want to build my own mounting hardware from somewhere like home depot. Any suggestions on commonly used materials for mounting?


Thanks for everyone's help in advance!

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New member, have some specific set up questions

    1 shading in even only half of 1 pv in a string will be detrimental to the whole string.
    2 i recommend you aim them south and at an elevation roughly at your latitude +15 degrees and at least 6 inches of clearance. i have used 1/8 in aluminum angle to mount my pvs singly. i would go with 1/4 in for trying more than one and you could also get either aluminum pipe (strong thick and expensive) or use 10ft fence poles/tubing in conjunction with the aluminum angle. you will need stainless steel hardware and an aluminum ground lug like this on each pv, http://store.solar-electric.com/gbdbtsopagrl.html
    you do want strength and durability as pvs can act like expensive sails during high winds and watch out for different metals contacting each other as that can cause galvanic reactions (rust) unless using the same metal or stainless steel.
    i'm sure others will chime in here and i believe solar guppy had a good pic of his old ground mounted setup that could give you some ideas too.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: New member, have some specific set up questions

    Couple of questions

    Why are you doing a battery system rather than a gird tie? Battery system roughly doubles the cost per kwh AND reduces efficiency.

    Why are you installing the panels flat? Proper tilt for you lat. will greatly increase you out put.


    Any shading on any series string will significantly reduce out put of that string, possible to almost zero.


    I urge you do read and understand as much about all of this, to avoid the ready fire, aim, sydrome.


    Tony
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: New member, have some specific set up questions
    azcrash wrote: »
    2. I will be doing the panels flat (well about 3 inches high to allow heat to escape) on the roof, and my roof is slightly slanted down. The mounting equipment sold online seems to be way over priced, and the lower priced stuff looks cheap. I want to build my own mounting hardware from somewhere like home depot. Any suggestions on commonly used materials for mounting?



    Greetings:

    Yes, mounting equipment sold online is way overpriced. So do yourself a favor: First, use aluminum; it is more expensive than other materials but it is a lot better. Second, go to one of those stores that sell aluminum for door and screens manufacturers, They have very good material, and at reasonable prices. Third, do pay attention to niel, boB, and the other guys in this forum, they really know what they are talking about.

    Additional: The tilt of the panels is indispensable (is this the correct word in English?), if you want to take advantage of all the panel’s potential (specially in winter time.)
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: New member, have some specific set up questions

    Unless you need un-interruptible power for your house, skip the batteries, and the M60, and get a Grid Tie inverter. You will go from harvesting 50% to about 95% efficiency. Big losses in the battery charging.

    Get the panels at least 6" off the roof for better air circulation. Cooler panels produce more power.

    Tilt the panels to the proper angle for your location.

    Implement energy conservation (CF lamps, thermostat settings, clean your air filters in HVAC system, thermal windows) and then you will start saving money
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: New member, have some specific set up questions
    1. The panels are 24 volts, and I have 6 of them. To reduce wire size, I would like to have 3 each in series, so have 2 72 volt panel "banks".

    ... a outback m60... aims pure sine 1500 watt inverter... live in the Phoenix Arizona metro area...
    This may not be a good idea. Can you tell us exactly which "24 V" modules you're planning to use? Also, are you planning on using the 12 V inverter ot the 24 V model?

    More later,
    Jim / crewzer
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: New member, have some specific set up questions

    I have about 12kw of PV using these 1.50 a piece Home Depot Gutter clips to mount my panels to the roof. 4 hurricanes and one tornado later no issues

    On the frst 6kw, I directed mounted to the panels, on the last 5kw added, I used the clips to secure 2x2 sluminimum sreen rails and then the solar panels to the rails.

    Probably have less than 1K into all the racking for over 86 panels
  • System2
    System2 Posts: 6,290 admin
    Re: New member, have some specific set up questions

    icarus,

    I am doing battery vs grid tie because I am also using the system as a backup when the power goes out.

    I am doing the panels flat because first my HOA says thats the only way they can be installed, and I am in a condo with a sloped west facing roof.

    Even if I could get by the HOA, I would still do them flat though. I know south facing panels are best, but I live in a high crime area and also want them flat because you cant really see them flat. I dont want punk kids stealing or throwing rocks to break them, and accept lower output to keep them from being visible.

    As for the grouping of the panels, would you just suggest keeping them all in parallel (24 volt) rather than 3 in series (72 volt) in case shade does hit one of the panels?

    crewzer -

    I am using 180 watt sun power 24v panels. m60 will do 24v as well, and the inverter is the 24v inverter, but should not matter since the m60 can output 12v as well :)


    Also thanks for everyone's input so far, I appreciate the info!!!
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: New member, have some specific set up questions
    azcrash wrote: »
    I am doing battery vs grid tie because I am also using the system as a backup when the power goes out.

    WHAT is it that needs battery backup? Computer ? Fridge? Iron Lung? Main Air Conditioning?

    How long do you need it to go for?

    1080w of panels, flat on a roof, is a pretty minimal system, and if you can translate most of that power into the grid, with grid tie, you will be far enough ahead of the game, you can buy a generator for the long outages.

    Also, someone has mentioned a way to use the attic, as a way to cool the panels, cutting a hole in the roof, beneath each panel, to let the attic air vent out, and cool the panels. I don't know if it would work in your case or not. Just an idea. Flat on the roof, with low clearance for air, will get pretty hot, and reduce output a lot.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2
    System2 Posts: 6,290 admin
    Re: New member, have some specific set up questions

    Solar Guppy,

    Those clips are pretty nifty looking. Do you get your rails from a store like home depot, then drill holes? I assume no holes needed for the clips but to connect to the roof - unless the rails have holes pre-drilled.

    Also, what are you using to stand the panels off the roof, then secure to the roof? I like the simplicity and effectiveness of your mounting system.

    Mike90045,

    the original reason I started looking into solar is because my area has power outages that can sometimes last quite a while. I am doing a 1080 watt system and going to use it for only 1-2 rooms, to for one keep my fridge on during power, my tv on, although that is not really needed but nice to have, but most importantly, to power a window 500 watt air conditioner.

    There was 3 days of power outages in a row this last summer. It got over 125 inside the house. Had to go stay at a hotel during these days. So if I have my 500 watt window AC unit, it would never keep the whole house cool but would keep one room livable for a couple of days.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New member, have some specific set up questions

    it sounds to me like you just need a large backups for certain things like the fridge, a few lights, and maybe 1 a/c unit. pvs could help with the charge to it, but i suspect it would not replace all that you use being mounted unoptimally. even with a good southerly exposure aimed at the sun you won't replace all that you'll use with that 1kw of pv. a fridge, although a large appliance in terms of energy consumption, is somewhat doable as they are typically 1-1.5kwh per day. the lights too if using cfls and shutting them off when not being used is quite doable. now an a/c unit going all of the time at .5kwh will kill everything in short order for that's 12kwh per day. the battery system will be large to accomodate all of this for even for 1 day and 3 days would be a better goal. the battery system will be at least 2x the ah capacity as the loads will require as you don't want your batteries falling below 50% dod.
    it may be better to get a generator to run these things and buy a security camera system and alarm system and this may be used in conjunction with a smaller ups system(still large if running a/c) for you don't want to run the genny during the night as you'll want to keep peace with the neighbors and take away the chance for a thief to steal the genny during the night as you'll drag it inside.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: New member, have some specific set up questions
    The panels are 24 volts, and I have 6 of them. To reduce wire size, I would like to have 3 each in series, so have 2 72 volt panel "banks".

    ... a outback m60... aims pure sine 1500 watt inverter... live in the Phoenix Arizona metro area..


    I am using 180 watt sun power 24v panels. m60 will do 24v as well, and the inverter is the 24v inverter, but should not matter since the m60 can output 12v as well :)
    I can’t find specs for the SunPower 180 W module.

    The record low ambient temperature for Phoenix is 16 F, so the NEC 690-7 TCF is 113%. This means that to stay under the 150 V max limit (or 141 V operational limit) for the MX60, the array’s STC Voc should not exceed 150 V (or 141 V) / 113% = 132.74 V (or 124.77 V).

    For three modules wired in series, the STC Voc spec for an individual module should not exceed 132.74 V / 3 = 44.24 V, or 124.77 V / 3 = 41.59 V. I recommend you check the module specs… 41.59 Voc is low for a “24 V” module.

    The 150 V max limit applies to all of the popular "big" MPPT controllers at present, along with popular DC circuit breakers used in PV combiner boxes.

    For either 24 V or 12 V battery systems, wiring the array as 2 (“24 V” modules in series) x 3 (series strings in parallel) will usually work just fine (but, see note below). The MX60 will operate a bit higher efficiency from a 48 V array (~60 Vmp operational) for 24 V or 12 V system that it would from a 72 V array (~90 Vmp operational). This gain may offset some of the loss in the wiring from the array to the controller. Check the efficiency charts in the MX60's user manual.

    However, the selection of the inverter DC voltage does indeed matter. A 1,080 W STC PV array exceeds the MX60’s maximum power rating (800 W) for a 12 V system.

    Note that the MX60 is primarily intended for negative ground applications. Check pg 61 in the user manual for an application note on the limitations of a positive ground system.

    Finally, don’t overlook any of the SunPower module specs or instructions. I don’t think you’ll find this on the reference data sheet, but check out the attached disclaimer in the instruction manual:
    4.2 System Grounding

    Important! For optimal performance, SunPower PV modules
    must only be used in configurations where the positive
    polarity of the PV array is connected to ground. Failure to
    comply with this requirement will reduce the
    performance of the system and invalidate SunPower’s
    Limited Power Warranty for PV Modules.
    For more information on grounding the system correctly, visit
    our website at www.sunpowercorp.com/inverters or contact
    SunPower technical support at 1-877-SUN-0123.
    HTH,
    Jim / crewzer
  • System2
    System2 Posts: 6,290 admin
    Re: New member, have some specific set up questions

    niel,

    Well first, I already have purchased all of the equipment so theres no going back now, I am already set up for non grid tie application.

    Second, in an emergency situation I would say screw the fridge. The only thing that would be used would probably be A/C unless I had extra electricity to spare.

    The window AC would serve 1 room the same that the main AC would serve the whole house, not being on all the time. Like the home AC, it would come on probably 1-2 times an hour, 10 min each when the sun is out. Much less when its not sunny. So, 1kw of panels would be fine for that application.

    Also, my batteries would keep me online at least a day, prob more, with no sun.

    I think the major reason I did not do grid tie with some sort of backup, is the fact that permits and grid tie equipment, as well as the electric company has to come out to install - would have cost more than batteries and other "off grid" equipment. So as a benefit I get backup power as well. I will be using most of the 1000 watts produced right away while the sun is shining anyway, almost no power will be used at night from this system.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: New member, have some specific set up questions
    azcrash wrote: »
    is the fact that permits and grid tie equipment, as well as the electric company has to come out to install - would have cost more than batteries and other "off grid" equipment.

    You do know that if there is a grease fire in your kitchen, and it smokes up your house, that "non-permitted" alterations to the house (solar & batteries) may serve as an excuse to your insurance company to void your policy.

    Heaven help you if a battery melts down, and the fire department discovers a battery bank in your closet.

    Hopefully, your Ready, Fire, Aim ! eagerness won't be too costly.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: New member, have some specific set up questions

    IMHO, with 1080 watts of panels, figuring average efficiencies, hour of sun et. I would be surprised to see you getting more than ~ 400-500 (useable) watt/hours/day with such a system. (Improperly aimed, over heated panels, inverter/controller efficiencies etc).

    I understand wanting to stay away from the permit issue, and the HOA, but I think, quite frankly, you are a victim of ready, fire, aim. After you factor in the life cycle cost of the batteries, which will most likely be chronically undercharged with a shorter life as a result, you will find that you have made some expensive mistakes.

    I also think this system may not even START, the ac unit, it certainly won't run it for very long. Add on the other loads you suggest and it will grind to a halt quite quickly.

    I also question how your system is going to be wired, if not grid connected. Are you going to have strings of cords running throughout the house? How are you going to fuse them etc? I suggest that you could also be running into some insurance issues should something go wrong. How are you going to make your battery bank safe, both from leakage, but also from fire/explosion? How are you going to vent the batteries?

    My point of all of this, is that it is much better to think things through thoroughly before spending money that one can't get back. Too many people think that they can give the power company the old heave ho by buying a few solar panels without knowing what is really involved.

    Every once in a while I think we need to be a bit more blunt to well meaning, but ill informed newbies. I think sometime we lead people on even though we (the "experts") think a project is ill concieved.

    (Please, no offence to anyone,,,the object of this site it to inform people about Solar energy, both the good and the bad).

    Tony

    PS Mike beat me to the insurance issue while I was writing,,,but I'll keep it in just to belabour the point!
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New member, have some specific set up questions

    one last thought here is that you indicated the temps can get to 125 degrees inside and you think that window unit usn't going to run 24/7? just the heat infiltrating from the other rooms would insure it to run constantly. we're just trying to help you understand what you're really up against and i wish you luck in it.
  • System2
    System2 Posts: 6,290 admin
    Re: New member, have some specific set up questions

    icarus and mike90045:

    I really appreciate any positive feedback offered, even if I don't like it or I am shown I am wrong. But I kinda feel more of an attack then being provided with help


    Mike -

    I got the system in the first place for emergency prep, lower energy costs was a obvious close second reason for installing.

    I am fully aware of insurance and all other things, this is anything but ready fire aim - i have been looking into these items years ago (hell, I even started getting scrap broken panels from craigslist, building my own panels, and testing with those), I am just now proceeding with install, and that is what I need help with, the install - not what I should have done different.

    There are a lot of things I would change with my exact system if I had a south facing roof, more land, lower crime, different intentions, no HOA, and so on, but like many people, I do have restrictions and doing my best to work with what I currently have.

    icarus -

    I get 7.5 hours of sun a day.

    Per help provided on the forum, I am looking into different ways to mount the panels, still flat but raised - this is the info I need help with, these types of suggestions.

    The system will start the AC. I have researched all of this. My surge rating on the inverter is 5000 watts, 1500 continued use. The AC unit is 2000 watt surge, 500 continued use. I have even tested this, and have had no problems starting the AC from the inverter in test situations.

    I had stated that I will be using the power in 1-2 rooms - the system with batteries will be in its own closet enclosure - one small hole will be drilled into the wall to the closet for the power line.

    I am using AGM batteries, which do not need vented.

    My point being, I have spent a VERY long time planning and looking into different situations. I am not ready fire aiming by any means. I simply need help with the install, any suggestions welcomed including constructive feedback.

    So back to my original questions, I would love suggestions for cheap (good) mounting options, hate to pay for overpriced mounting equipment when local shops have the products I need.

    I also would love any more feedback on how to wire the panels. It kinda appears from the feedback I have so far, that I should not do any of it in series, but each panel in parallel. I dont like this idea because of the larger wire needed, but I guess it would be better to go for larger wire @ 24 volts than smaller wire @ 72 volts with the risk of one panel being shaded and lowering efficiency for the entire array.
  • System2
    System2 Posts: 6,290 admin
    Re: New member, have some specific set up questions
    niel wrote: »
    one last thought here is that you indicated the temps can get to 125 degrees inside and you think that window unit usn't going to run 24/7? just the heat infiltrating from the other rooms would insure it to run constantly. we're just trying to help you understand what you're really up against and i wish you luck in it.

    The reason they were 125 inside is because it was VERY hot all day and night, then it finally got to that temp, and outside it was 115. Basically very hot but only 10 degrees hotter than outside, due to the oven effect.

    My house is VERY insulated as well, never even have to turn on the heat in the winter.

    The only reason I have my window AC in the first place is my main AC unit went out - had to get it replaced. In the mean time I used the window AC and it worked fine then for 1 room, and this was also in the summer.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: New member, have some specific set up questions

    Rebuff, well taken.

    As for mounting go to a wholesale HVAC outlet, (Gensco, or eq) and get a bunch of unistrut. Steel with drilled holes, comes in angle irons, as well as channel iron, as well as square tubing. with a bunch of hardware store bolts, you can bolt the whole thing together in whatever configuration you wish.

    If the wholesaler won't sell to you over the counter, you can get most of the stuff at Home Depot.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New member, have some specific set up questions

    Spencer,

    Nobody is trying to attack you--they really are concerned that you are expecting way more from your system than is really possible... And the trade-offs you are making are not helping... Most of the people here are doing solar/conservation to save money and conserve (in the true sense of stepping lightly on the environment), and some preparation for emergencies.

    So--to take some of the issues... Laying panels flat--yes, you will loose some energy by doing this--but for your area, the bigger issue is that panels that don't have roughly a 15 degree tilt (or higher), tend to accumulate leaves and dirt... You will probably have to clean them more often because of this (and need good access for water and broom to wash).

    Lastly, regarding battery venting--Yes AGM's don't normally output hydrogen gas--but the room/enclosure still should be properly vented--overcharging AGM's will cause them to vent hydrogen gas (i.e., failed charge controller).

    Regarding wiring of panels--You have picked panels that require positive ground (if negative grounded, their outputs fall pretty dramatically because they build up charge--and the effect of negative grounding does not damage the panels--positive grounding fixes this issue)--so you will have to follow Outback's/ Jim's-Crewzer's information on how to do positive ground for your MX 60... You will also have to check out the rest of the electronic.

    For series/parallel panel connections, you have to match the panels against the Charge Controller and battery bank voltage...

    Looking at Sunpower 200 watt panels (180watt???)... When they are cold, Voc~52.6v (14F) and Vmp~32.7 (110F)... So, you can put 1 or two panels in parallel (3 is probably to high and will violate the MX 60 warranty on cold days). 2 panels in series should be OK for a 12, 24 or 58 volt battery bank (you will need to confirm yourself--I am not affiliated with OutBack--and I don't have the specs. for your 180 watt panels--my numbers are just a guess).

    For how much power you can collect... Using this link (using defaults for Phoenix AZ, 0.52 derating for battery based system, array mounted flat); you will collect somewhere around 90-100 kWhrs per month for the "summer" months--or have about 3 kWhrs per day of useful work...

    If you have a small A/C system that can run on a 15 amp service--see about getting a Kill-A-Watt meter... You can plug the A/C and see how much power per day it really takes.

    Glad to hear your home is very well insulated--but be aware that not needing to heat in the winter can also because of lots of electrical use heating your home (TV's, computers, Fridge, Freezer, etc.)... Heavy electrical use in the summer will also heat up your home (and require more A/C).

    If you do not have double pane windows with low E glass--I would suggest looking into put them in... On my old home, just changing the 50 year old windows out with double pane vinyl windows dropped the temperatures in our west facing bedrooms by 20 degrees F in the summer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: New member, have some specific set up questions

    Thanks for the responses, I know intentions are good on the responses, I hope I was not too harsh - I mean I would not even be on these forums if I knew all the answers and I for sure appreciate any knowledge provided.

    Prior to the responses to this post, I didnt know that so much power was zapped by keeping the panels close to the roof - thinking about this issue I think I have figured out a way to mount them so they are at a 45 degree angle pointing south, and still are not very visible from the ground and my HOA will have to really look close to see they are mounted in this way.

    I also think I have way over-thought the mounting hardware. The stuff I was thinking of using now that I think of it, could have mounted a large elephant on the roof :cool:

    So, at least for this "phase" of the install I really need help with two issues:

    1. Cant decide between 24 and 48 volt - for 48 volt I would put two panels in series, but there will be about an hour a day where they will be shaded, but a huge palm tree a few neighbors away - any suggestions or feedback of course welcome.

    2. Now that I will probably be doing these at an angle, any hardware I was thinking of using will not work. Gutter clips were mentioned, does anyone have pictures where these are used?

    Thanks for the info on the unistrut hardware, ill have to check my local hardware stores for that.

    Mounting to the roof - Does anyone have any tips or tricks on this? I was planning on taking a section of 2x4, and screwing it between two rafters, drilling a hole through the roof, into the 2x4, then large bolt starting in the attic and going up to the roof, then bolt unistrut or other material to this.

    If this sounds good, how big of bolt and how many holes would I need to make in the roof to mount my system? I have 6 panels, each one being about 3 ft x 6 ft.


    Again, thanks for any help.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New member, have some specific set up questions

    Regarding Panel Angles... Play with the Solar Calculator link I provided earlier...

    Putting the panels up to 33.4 degrees will give you an extra ~16% power over the year--but, if you need summer power (A/C)--then putting them back down at 15 degrees will actually give you a bit more power during the summer...

    Shading of panels is an issue no matter what... If you have two or more strings in series, then shading a part of even one panel will drop the production of that string to near zero amps... (think of batteries in parallel--if one of them goes dead in a series string, the other strings will pick up the load).

    -Bill

    PS: Sometimes you cannot avoid the shade and have to take what you get... In my previous link, you can output hourly results and figure out how much shading will cost you on an hour by hour basis... If you have good sun from 9pm-3pm (all year long)--you are capturing the majority of the energy. And, remember to watch the summer/winter shading changes too.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New member, have some specific set up questions

    in mounted to your roof, the bolts should go straight into the roof and into the large 2 bys that are used for the roof framing. on a flat roof you may have to figure out how to keep that from leaking as i'm not a roofing expert. you may need to consult a good roofer for advice on this as you certainly don't want to cause a problem with the roof. anybody else have knowledge on mounting on flat roofs? you also need to get the wire into the condo. how are you planning to do that?

    edit to add: if you have lots of stone on the flat roof that will give you an option of running legs out to be held by the stone and no intrusion to the roof will be made. that is alot of stone though.

    btw, if you overcome the positive ground problem with the mx60, having the series strings of 2 are fine and you could parallel more strings of 2 with it.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: New member, have some specific set up questions
    btw, if you overcome the positive ground problem with the mx60, having the series strings of 2 are fine and you could parallel more strings of 2 with it.
    This may be a semantics issue, but I’d suggest that the “positive ground problem” lays with the SunPower PV modules. Sunpower claims improved performance with this architecture, and the battery-less grid-tie inverters sold by SunPower are configured for positive ground.

    However, for applications involving charge controllers, negative ground is the norm. All OutBack charge controllers are designed primarily for negative-ground applications, and Xantrex states that “the (XW) Charge Controller is designed to work only with negative-grounded electrical systems.” Other big MPPT controllers from Apollo and Blue Sky also appear to be intended for negative-ground applications.

    HTH,
    Jim / crewzer
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: New member, have some specific set up questions

    You ~can~ ground the positive PV lead if you MUST. Just do NOT ground anything else in the system if you do !

    I still wonder if there might be another way around this PV efficiency problem besides having to ground the positive PV terminal. Don't know what that might be, exactly.

    boB :D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New member, have some specific set up questions

    boB,

    As far as I know and understand (which is not that much)--the Sunpower panels must be positive grounded--or they will loose much of their output (for any panels that are a net voltage above ground)... One example was a 200 watt panel that dropped to a 140 watt output.

    Here is a thread with details on the reasons that SunPower needs a positive ground (negative grounding will not damage the panels--just reduce their output until they are positively grounded).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: New member, have some specific set up questions

    Spencer, what is your existing roof slope right now? When we built I added 2x4's the flat way next to the 2x6 roof truss, then screwed them through the “vertical” 2x6 in to the “horizontal” 2x4 to hold them in place. I did that after the OSB roof decking was on. It is above our garage and the pitch is 9 in 12 (about 30*). Then I ran 1/2" stainless steel threaded rod up though the added 2x4 through the roof on 4 foot centers in each direction. The rod extended up about a foot above the OSB. Then the roofers came along and added more tar around them and put the asphalt roof right around them all. I thought they were going to really complain about them, but they said they were pretty easy to work around.

    Above that I just used cheap 8 foot sections of angle steel with all the slots and holes in them overlapping to make up the horizontal supports, just about every hardware store has them. Then on the underside of the panels I put the same angle steel and they just nest in to one another and then I use smaller nuts and bolts to keep them in place. From doing a similar thing in our first house I went to all stainless steel nuts, bolts, washers, and threaded rod. It costs a bit more, but it is really a pain when you have a small nut under the panels rusted in place. I also jack up the top end of our panel in winter to get them to about a 55* tilt.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New member, have some specific set up questions
    boB wrote: »
    You ~can~ ground the positive PV lead if you MUST. Just do NOT ground anything else in the system if you do !

    I still wonder if there might be another way around this PV efficiency problem besides having to ground the positive PV terminal. Don't know what that might be, exactly.

    boB :D

    boB,
    do you happen to know what happens to them without a ground if it would still degrade?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New member, have some specific set up questions

    Niel,

    From reading the papers I posted the links to... It is the panel's voltage in relationship to the "earth's" field... So, if they are ungrounded--there still would be some sort of leakage path wrt to earth--so the panels will float to some voltage...

    The earth's electric field is roughly 100 volts per meter (air "positive", ground = 0 volts)... So a positively grounded array would hold the panels at "negative" voltage wrt to the earth's electric field.

    If you had a set of panels floating--they would eventually take the "positive" voltage of the earth's field--so I would guess that they would still have their output fall over time.

    NOTE: The earth's field is high variable and can change polarity (I think that lightning bolts, for example, can be either polarity, and obviously, the earth's field rises dramatically just before a strike).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: New member, have some specific set up questions
    BB. wrote: »
    boB,

    As far as I know and understand (which is not that much)--the Sunpower panels must be positive grounded--or they will loose much of their output (for any panels that are a net voltage above ground)... One example was a 200 watt panel that dropped to a 140 watt output.
    -Bill

    Bill, I know this, but was just mentioning that you can ground the positive lead of these panels with an MX60 if you HAVE to.

    I've read the papers from Sunpower on this effect. I don't really care for this newly discovered "problem" though. Sounds like these modules are great for 48V telecom sites. Not for use on airplanes or space stations. I think it's not JUST Sunpower that has a problem of this sort either. Having a brain fart at the moment and can't remember who this was... Who was it from last week where this was also a problem but the manufacturer said you HAD to positive ground their panels ?? Or maybe you HAD to negatively ground their panels ? Mind is gone. Too much lunch. Might have not been this forum anyway. Oh well.... Will roll over and go back to sleep now.

    boB :D